The use of waste, fine-grained carbonaceous material in the process of copper slag reduction

The article presents the results of the research on the reduction of the high-copper slags produced in the single-step Outokumpu blister copper production process, carried out by KGHM Polska Miedz. The company is the fifth largest blister copper producer in the world. The tested slags containing 12–16 wt%. Cu, < 4 wt% Pb and up to several wt.%. Fe are processed in an electric furnace using coke breeze as a reducing agent. As an alternative reducer, a fine-grained carbon-bearing waste material (the so-called flotoconcentrate), produced in the process of enrichment of coal sludge, has been proposed. The aim of the presented investigation of the slag processing was the recovery of the valuable metals (Cu and Pb) and the secondary materials that could be directly used in the various branches of the economy (so called secondary slag). The results of the conducted experiments show that the quick coke, traditionally applied in this process, can be replaced with pellets made from the waste flotation concentrate. The yield of copper removal from all the slag batches examined was 96–98%. The compositions of the Cu–Pb–Fe alloys and slags obtained in the experiments were acceptable, since the degree of copper and lead removal from the primary slag remained within the limits typically observed for the industrial-scale processing. Since the final copper content (wt.) in the waste was lower than 0.4 wt%, and the final lead content (wt.) was less than 0.5%, the slag constitutes a waste material that may be used for road making and in the building industry. The proposed approach may bring the cost down up to 50% in comparison to the commonly used carbon-based reducing agents. [Display omitted] •The concentrate from coal flotation in the copper slag reduction process allows to shorten the process time.•The Coal flotation concentrate increases the speed of the process by accelerating the coalescence of metal droplets.•The use of carbon waste is consistent with the goals of sustainable development.